Reddit:

https://redditmetis.com/user/[YOUR USERNAME HERE]

Hexbear:

(Python script using @congressbaseballfan as an example since she asked originally)

USERNAME = 'congressbaseballfan'

import string
import json
from urllib.request import Request, urlopen as fetch

def fetch_json(url: str):
    request = Request(url)
    request.add_header('User-Agent','Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)')
    request.add_header('Content-Type','application/json')

    with fetch(request) as response:
        return json.load(response)

def word_count(s: str) -> int:
    no_punctuation = s.translate(str.maketrans('', '', string.punctuation))
    return len(no_punctuation.split())

url = f'https://hexbear.net/api/v1/user?username={USERNAME}&sort=New&limit=5000&saved_only=false'
data = fetch_json(url)
comments = [c['content'] for c in data['comments']]
total_count = sum(word_count(c) for c in comments)
account_created = data['user']['published'][:10]

print(f'{USERNAME} has written {total_count} words since {account_created}')